Screening, Diagnosis and Monitoring

#Screening identifies who may need further assessment

WHO describes screening as identifying people in an apparently healthy population who are at higher risk of a condition so an early intervention can be offered. In cancer screening, NCI describes testing asymptomatic people and notes that some positive findings require further procedures to rule out or confirm cancer. A positive screen is therefore not automatically a final diagnosis.

The intended population and complete pathway matter. UK screening appraisal criteria consider a validated test, agreed further investigation, effective intervention, acceptable harms and resources for follow-up. Screening is more than making a test available. These are programme-level concepts; this page does not decide who should participate in any particular programme.

Evidence: WHO: screening programme benefits and harms / NCI: cancer screening evidence overview / UK National Screening Committee: programme appraisal criteria

#Diagnosis and monitoring ask other questions

Diagnostic testing investigates a suspected condition, often alongside symptoms, examination findings, health history or an earlier result. Monitoring follows an established condition or treatment to help assess whether it is changing or whether treatment is working. MedlinePlus describes both uses and emphasizes that a laboratory result is only part of the clinical picture.

STARD lists screening, diagnosis and monitoring as different intended uses. Its guidance asks authors to explain the purpose and role of the test because these affect study design and interpretation. Evidence from one purpose should not simply be carried into another. This page does not set a testing schedule, interpret a change or advise changing treatment.

Evidence: MedlinePlus: understanding lab results / STARD 2015: explanation and elaboration

#Separate false alarms from overdiagnosis

A false positive suggests a target condition that is not present under the appropriate diagnostic definition. Overdiagnosis is different: screening finds a condition that would not have become clinically apparent or caused harm during the person’s lifetime. NCI explains this distinction for cancer and describes the possible harms of additional investigations and treatment.

False-negative results can also give false reassurance. The balance depends on the particular programme, its population and the follow-up pathway, not just how many abnormalities it finds. An accurate detection can still lead to harm without useful benefit. These concepts are reasons to assess evidence and support informed choices, not reasons to conclude that all screening is harmful or beneficial.

Evidence: NCI: cancer screening evidence overview / UK National Screening Committee: programme appraisal criteria / FDA: reporting diagnostic test performance

#Earlier detection is not the same as longer life

NCI explains why survival measured from the date of cancer diagnosis can mislead. If a diagnosis occurs earlier but the time of death does not change, the measured survival interval grows without life being extended. This is lead-time bias. Screening can also preferentially detect slower-growing cancers, which changes the mix of detected disease. These are cancer-screening examples, not assumptions about every diagnostic test.

Evaluate outcomes that fit the programme’s purpose, with a suitable comparison group and attention to harms. Finding more early cases or reporting longer survival after diagnosis does not alone prove that screening reduces deaths. This page supplies no disease-specific screening ages, intervals or thresholds and no advice to accept, decline, repeat or stop an individual test.

Evidence: NCI: cancer screening evidence overview / NCI: what screening statistics mean / UK National Screening Committee: programme appraisal criteria

Source note

The sections above were checked against the linked sources. No clinical review has been performed. This is general research education, not a clinical guideline.